1. Field of the Invention
This invention relates generally to a method of making a coil spring and an apparatus therefor. More particularly, this invention provides a method and apparatus for winding a selected length and diameter of a wire material into a spiral configuration by using a mandrel so as to automatically make a coil spring, particularly a large compression spring having seats at its opposite ends.
2. Description of the Prior Art
In making coil springs, two types of wire material, cold and hot, are usually employed dependent on the size of coil springs to be formed. First, cold wires are used to permit cold working on small springs formed of relatively thin or small-diameter wires. Second, hot wires previously heated to a predetermined high temperature are used to permit hot working on large coil springs formed of relatively thick or large-diameter wires. In either form of manufacturing process, it is necessary to accurately set and maintain the feeding position and posture of a wire material relative to the mandrel so that the winding requirements are satisfactorily fulfilled. Especially, in manufacture of springs having seats or wedge-shaped rolled portions previously formed on their opposite ends, it is essential that the orientation and position of such rolled portions be held accurately to suit the winding requirements.
The previously known art of manufacturing springs will now be described briefly. In general, the "shiftable wire-based winding process" has hitherto been employed. FIG. 45 is a schematic illustration of such a process, and as may be seen, a mandrel M' on a winding machine, being set at a fixed position and orientation, is rotated at a constant speed in a desired direction, while a wire on a feeding machine is fed toward the mandrel M' and moved in the axial direction of the mandrel, thus shifting its direction of advancement (the angle of feed) progressively to suit a selected pitch of the spring to be wound by the mandrel M'.
However, such a process includes a number of potential problems. Normally, the wire on the feeding machine has to be gradually shifted in the axial direction of the mandrel, requiring a relatively complex and large machine and hence a considerably large area for its installation. This runs counter to the general tendency toward the simplification of such manufacturing lines. In addition, since the direction of wire advancement is shifted by the movement of the feeding machine (in other words, the direction of wire advancement is selected dependent on the movement of the feeding machine), the prior art process fails to accurately set the posture and angle of wire advancement relative to the mandrel, and deformation, such as bend and deflection, of the wire can result. Therefore, the process still has a number of problems to be overcome in winding the wire properly as desired and manufacturing high quality springs having accurate and stable shape (particularly in terms of pitch) continuously at high speeds.
Further, the prior art method of manufacturing springs, where wires are shifted during their advancement, entails considerable danger such as during a hot forming process. Namely, when wires with rolled portions are processed, a plurality of operators are required to check and correct the orientation of the rolled portions at an appropriate stage in the latter half of the winding process. At that time, no matter how skillful they are in such a correcting operation, they are liable to danger such as a burn, as the operation is carried out during the shifting movement of hot material. In addition, the important considerations are the safety and prudence in performing such an operation; and reliable cooperation between the machine operators. Apparently, all of these factors have contributed to failure to speed up the overall manufacturing operation and to improve the productivity.